This invention relates to a titanium-tungsten (titanium-tungsten) target material used to form a barrier metal layer or the like for use in semiconductor devices and to a method of manufacturing the titanium-tungsten target material.
With the increase in the degree of integration of large scale integrated circuits (LSIs), a problem of aluminum wiring migration, such as contact migration of diffusion precipitates at contact portions of aluminum wiring and a silicon semiconductor substrate, has arisen. To cope with this problem, barrier metal layers have recently been studied.
A titanium-tungsten thin film (typically composed of 10 wt %, of titanium and the balance of tungsten) is often used as a barrier metal layer, and a method of sputtering a target is adopted to form such a titanium-tungsten thin film.
In general, a titanium-tungsten target material for the thin film is manufactured by blending a titanium powder and a tungsten powder and hot-pressing the blended powder.
However, titanium powders used as raw materials for the conventional titanium-tungsten targets have a large oxygen content, and the oxygen content of targets formed from such raw materials is necessarily high.
Such high-oxygen-content targets are disadvantageous because oxygen is liberated during sputtering to cause cracks in the target, oxidation of formed films, and variations in film quality.
U.S. Pat. No. 4,838,935 discloses a method for reducing the oxygen content of a titanium-tungsten target or a fact that the formation of a high-density low-porosity target as well as reductions in the carbon and oxygen contents can be achieved by replacing at least a pair of a titanium powder with hydrogenated titanium or by using a tungsten powder having a binodal grain size distribution and a hydrogenated titanium powder or a mixture of a hydrogenated titanium powder and a titanium powder.
JP-A-63-303017 also discloses a method for reducing the oxygen content of a titanium-tungsten target. In this method, a tungsten powder and a hydrogenated titanium powder are blended together and hot-pressed after or while being dehydrogenated.
The use itself of the hydrogenated titanium powder is effective in preventing oxidation and is also capable of limiting the amount of oxygen picked up during milling because the hydrogenated titanium powder may be more suitably milled with less contamination by oxygen as compared with the ordinary titanium powder.
It has thus become possible to obtain titanium-tungsten targets having an oxygen concentration as low as 900 pm or less.
As has been described, research has been made extensively to reduce the oxygen content of titanium-tungsten target materials.
The above-mentioned publications, however, contain no suggestion as to how the structure of titanium and tungsten constituting a target affects sputtering, that is, they do not disclose at all that the alloy structure, particularly the presence of a titanium phase, relates to the occurrence of particles during sputtering.
Recently, with the development of semiconductor products having thinner conductors formed at a higher density, a new problem has arisen with respect to a sputtering process using the above-mentioned low-oxygen-concentration titanium-tungsten target in that large particles attach to a thin film formed by sputtering to cause disconnection of electrode wiring conductors.
The generation of such particles cannot be prevented as long as only the method for reducing the titanium-tungsten target oxygen content is used.
To solve this problem, the inventor of the present invention has examined in detail the relationship between the target structure and the generation of particles, and has found that coarse titanium grains relate to the generation of the particles. That is, the inventor has ascertained, as one of the reasons for the generation of particles, a fact that in the presence of both titanium and tungsten, titanium having a light atomic weight is selectively sputtering, and that tungsten grains contained in or in the vicinity of coarse titanium particles are scattered as large particles from the target material.